This invention relates to a print head for use in printers having self-cleaning features and a printer having self-cleaning features.
Ink jet printers produce images on a receiver by ejecting ink droplets onto the receiver in an imagewise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on a receiver medium such as plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
Many types of ink jet printers have been developed. One form of ink jet printer is the xe2x80x9ccontinuousxe2x80x9d ink jet printer. Continuous ink jet printers generate a stream of ink droplets during printing. Certain droplets are permitted to strike a receiver medium while other droplets are diverted. In this way, the continuous ink jet printer can controllably define a flow of ink droplets onto the receiver medium to form an image. One type of continuous ink jet printer uses electrostatic charging tunnels that are placed close to the stream of ink droplets. Selected droplets are electrically charged by the charging tunnels. The charged droplets are deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them. A gutter may be used to intercept the charged droplets, while the uncharged droplets are free to strike the receiver.
Another type of ink jet printer is the xe2x80x9con demandxe2x80x9d ink jet printer. xe2x80x9cOn demandxe2x80x9d ink jet printers eject ink droplets only when needed to form the image. In one form of xe2x80x9con demandxe2x80x9d ink jet printer, a plurality of ink jet nozzles is provided and a pressurization actuator is provided for every nozzle. The pressurization actuators are used to produce the ink jet droplets. In this regard, either one of two types of actuators are commonly used: heat actuators and piezoelectric actuators. With respect to heat actuators, a heater is disposed in the ink jet nozzle and heats the ink. This causes a quantity of the ink to phase change into a gaseous bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled onto the recording medium.
With respect to piezoelectric actuators, a piezoelectric material is provided for every nozzle. The piezoelectric material possesses piezoelectric properties such that an applied electric field will produce a mechanical stress in the material. Some naturally occurring materials possessing these characteristics are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate. When these materials are used in an ink jet print head, they apply mechanical stress upon the ink in the print head to cause an ink droplet to be ejected from the print head.
Inks for high speed ink jet printers, whether of the xe2x80x9ccontinuousxe2x80x9d or xe2x80x9con demandxe2x80x9d type, must have a number of special characteristics. For example, the inks should incorporate a nondrying characteristic, so that drying of ink in the ink ejection chamber is hindered or slowed to such a state that by occasional xe2x80x9cspittingxe2x80x9d of ink droplets, the cavities and corresponding orifices are kept open.
Moreover, the ink jet print head is exposed to the environment where the ink jet printing occurs. Thus, the previously mentioned orifices and print head surface are exposed to many kinds of airborne particulates. Particulate debris may accumulate on the print head surface surrounding the orifices and may accumulate in the orifices and chambers themselves. Also, ink may combine with such particulate debris to form an interference burr that block the orifice or that alters surface wetting to inhibit proper formation of the ink droplet. Of course, the particulate debris should be cleaned from the surface and orifice to restore proper droplet formation.
Ink jet print head cleaners are known. One form of ink jet print head cleaner is disclosed in U.S. Pat. No. 4,970,535 titled xe2x80x9cInk Jet Print Head Face Cleanerxe2x80x9d issued Nov. 13, 1990 in the name of James C. Oswald. This patent discloses an ink jet print head face cleaner that provides a controlled air passageway through an enclosure formed against the print head face. Air is directed through an inlet into a cavity in the enclosure. The air that enters the cavity is directed past ink jet apertures on the head face and out an outlet. A vacuum source is attached to the outlet to create a sub-atmospheric pressure in the cavity. A collection chamber and removable drawer are positioned below the outlet to facilitate disposal of removed ink. However, heated air is not a particularly effective medium for removing dried particles from the print head surface. Also, the use of heated air may damage fragile electronic circuitry that may be present on the print head surface.
Cleaning systems that use a cleaning fluid such as an alcohol or other solvent have been found to be particularly effective in removing contaminant from the surface of a print head. This is because the cleaning fluid helps to dissolve the ink and other contaminants that have dried to the surface of the print head. One ink jet print head cleaner that uses a solvent to clean portions of the print head is disclosed in commonly assigned U.S. Pat. No. 4,600,928 by Braun et al. This patent is directed to cleaning components within an ink jet print head of a continuous type. In Braun et al., an orifice plate is used to form ink droplets. These ink droplets are charged and are passed by a catcher that is selectively charged to attract droplets having a certain charge. The droplets that are permitted to pass the catcher are permitted to strike a media. During cleaning, a fluid meniscus of ink is statically supported along an axis that is generally normal to the orifice plate to form a meniscus between the charge plate, orifice plate and/or the catcher. This meniscus is ultrasonically excited to clean the orifice plate and charge plate and catcher. The ink from the meniscus is then ejected into a sump that is located at a cleaning station.
U.S. Pat. No. 5,574,485, to Anderson et al. also describes a cleaning station for cleaning a print head using an ultrasonically excited liquid meniscus. In Anderson, et al., the cleaning station comprises a cleaning fluid jet and a pair of vacuum orifices flanking the jet. During cleaning the jet is moved into a position that is proximate to the print head. The jet is separated from the print head by a distance, xe2x80x9ctxe2x80x9d. In Anderson et al., xe2x80x9ctxe2x80x9d is defined as being xe2x80x9cabout 10 milxe2x80x9d, 0.25 mm, or 250 microns. When the jet is so positioned, the jet defines a bulge of a cleaning fluid at the print head. A meniscus bridge of cleaning fluid is formed between the print head and the jet. Anderson et al., teaches that the print head is cleaned by scanning this meniscus bridge along the surface of the print head and by agitating the meniscus bridge using an ultrasonic vibrator. Cleaning fluid and any contaminants that are removed from the surface are entrained in the meniscus or left on the surface of the print head to be vacuumed from the surface by the vacuum orifices.
Thus, Braun et al. teaches that a print head can be cleaned in a non-contact manner using a static fluid meniscus and Anderson et al., teaches cleaning a print head using an ultrasonically excited meniscus that is scanned along the surface of a print head.
It will be recognized that it is often useful to apply mechanical force to clean contaminant that has dried to the surface of a print head or that is positioned within an ink jet orifice. In the prior art, a method known as wet wiping has been used to accomplish this end. In wet wiping, cleaning fluid is applied to the print head and a wiper is used to clean the cleaning fluid and contaminants from the print head. Examples of various wet wiping embodiments are shown in Rotering et al. U.S. Pat. No. 5,914,734. Each of these embodiments uses a cleaning station to apply cleaning fluid to the print head and mechanically wipes a wiper against the surface of the print head to clear contaminant from the print head surface. However, when wipers are used in this fashion, they can cause damage to fragile electronic circuitry and Micro Electro-Mechanical Systems (MEMS) that may be present on the surface of the print head. Further, the wiper itself may leave contaminants on the surface of the print head that can obstruct the orifices.
Thus, what is needed is a self-cleaning print head and a self-cleaning printer that have the cleaning benefits of both mechanical and fluidic cleaning while protecting the outer surface of the print head from damage during cleaning operations. What is also needed is a self-cleaning print head and a self-cleaning printer that cleans contaminant from the outer surface of the print head by applying mechanical force against the contaminant along more than one axis.
It is an object of the present invention to provide a self-cleaning print head that has the cleaning benefits of both mechanical and fluidic cleaning while still protecting the surface of the print head from damage during cleaning operations. It is another object of the present invention to provide a self-cleaning print head that cleans contaminant from the outer surface of the print head by applying mechanical force against the contaminant along more than one axis. These and other objects of the invention are accomplished by a self-cleaning print head. The self-cleaning print head comprises a print head body having an outer surface defining an ink jet orifice. A source of pressurized cleaning fluid is provided to generate a flow of cleaning fluid at the outer surface during cleaning. A fluid drain is provided to receive the flow of cleaning fluid. A movable flow guide defines a flow path from the source of pressurized cleaning fluid along the outer surface and ink jet orifice and to the fluid drain. During cleaning a translation drive moves the flow guide along a path that diverges from the flow path.
It is a further object of the present invention to provide a self-cleaning printer that has the cleaning benefits of both mechanical and fluidic cleaning while protecting the outer surface of the print head during cleaning operations. What is also needed is a self-cleaning printer that cleans contaminants from the outer surface of the print head by applying mechanical force against the contaminant along more than one axis. The self-cleaning printer comprises a printer body, a print head having an outer surface defining an ink jet orifice, a source of pressurized cleaning fluid to generate a flow of cleaning fluid at the outer surface during cleaning, a fluid drain to receive the flow of cleaning fluid, a movable flow guide defining a flow path from the source of pressurized cleaning fluid along the outer surface and ink jet orifice and to the fluid drain a translation drive for moving the flow guide along a path that diverges from the flow path.